In metal can manufacturing operations, the bottom of the can is customarily formed with a domer assembly in which a ram-mounted metal can blank is forced in succession against a clamp ring and domer tool to form an outer peripheral beveled or radiused edge in surrounding relation to a domed portion. In doming operations, it is important to establish a differential between the reaction force for resisting movement of the clamp ring and that required for resisting movement of the dome forming tool. Initially, the force of the ram will overcome the reaction force of the clamp ring to cause the clamp ring to be retracted; and then will continue to force the bottom of the can against the domer tool to result in an upwardly dome-shaped configuration in the bottom wall of the can. "Overstroking" occurs as the ram completes its working stroke prior to its return stroke and is important in causing the ram to bottom out at the end of the stroke to complete formation of the dome in the bottom wall of the can.
In the past, reaction forces have been generated through the use of mechanical springs acting either alone or in combination with fluidized pressure sources, such as, airbags or air cylinders. Representative of such approaches are U.S. Pat. Nos. 4,790,160 to B. E. Johansson et al, 3,760,751 to L. G. Dunn et al, 4,620,434 to S. Pulciano et al, and 4,930,330 to G. Weishalla. Moreover, it has been proposed in the past to utilize nitrogen pressure sources in die-stamping operations and, for example, attention is directed to U.S. Pat. Nos. 4,774,865 and 4,934,230 to B. J. Wallis, 4,815,718 to P. M. Kadis and 4,838,527 to D. M. Holley. In addition, U.S. Pat. No. 4,715,978 to W. L. Taube et al proposes the use of a nitrogen pressure source in creating different force levels acting across a piston and piston rod in forming a can end or blank. As employed by Taube et al, nitrogen gas is proposed as merely one type of fluidic pressure source in a different type of forming operation than the doming operation of this invention but in which the pressure exerted across an outer forming ring is higher than that applied across an inner concentric forming pad; and the fluid pressure is utilized more to load a mechanical spring which in turn applies the force to a knock-out lift ring to remove the formed can end.
In doming operations, it is desirable to maintain present reaction forces cable of withstanding high speed repetitive stroking of a ram in doming each can bottom. However, the utilization of springs creates particular problems in maintaining a preset reaction force over repeated doming operations. The same is true of many of the fluidized pressure sources employed and particularly those which rely upon airbags or air cylinders and this problem is exacerbated by the difficulty of gaining access to the reaction force-generating means whether in the form of springs or fluidized pressure sources for the purpose of servicing or replacement. Typically, such generating means are mounted internally as a unitary part of the domer assembly and require disassembly of the entire installation for repair or replacement. When overstroking is desired at the end of each working stroke, it is important that closer tolerances be established to assure that the overstroking will occur just as the ram bottoms out and prior to its return for the next working stroke; also, that there be a constant predetermined pressure when the ram or punch bottoms out. Under repeated doming operations, there is a tendency to lose the tolerances required as well as to experience pressure changes in generating the reaction forces needed for precise overstroking.
It is therefore desirable to provide for a domer assembly which is so constructed and arranged as not to require disassembly of the entire installation in order to replace or service the reaction force-generating means and specifically in such a way that the generating means can be attached independently to the domer assembly and automatically brought into alignment with the clamp ring and domer tool in performing doming operations. Furthermore, it is desirable to provide for such an installation in which the reaction forces are generated in an axial direction in direct opposition to and in alignment with the respective movement of the clamp ring and dome plug. Also, it is important that the domer assembly be readily adjustable for different length domer tools and to make any necessary adjustments in tolerances to achieve the overstroking required at the bottom or end of each working stroke.